Manufacture of semiconductor integrated circuits and other micro-scale devices typically requires formation of multiple metal layers on a wafer or other substrate. By electroplating metals layers in combination with other steps, such as planarizing, etching and photolithography, patterned metal layers forming the micro-scale devices are created.
Electroplating is performed with the wafer, or one side of the substrate, in a bath of liquid electrolyte, and with electrical contacts on a contact ring touching a conductive layer on the wafer surface. Electrical current is passed through the electrolyte and the conductive layer. Metal ions in the electrolyte deposit or plate out onto the wafer, creating a metal film on the wafer. The metal ions also tend to plate out onto the electrical contacts as well, which changes the electric field around the contacts, causing non-uniform plating. The metal plated onto the electrical contacts consequently must be removed, adding to the time requirements and complexity of the manufacturing process.
To avoid having metal ions plate out onto the electrical contacts, contact rings have been designed with a seal that seals the electrolyte away from the electrical contacts. The seal rests on the wafer surface radially inwardly of the electrical contacts, keeping the electrolyte away from the electrical contacts. Industry specifications for plating with a sealed contact ring increasingly require that the annular band at the edge of the wafer covered by the seal be as small as possible, currently towards about 1 mm. Some wafers have a notch in the edge of the wafer to indicate a specific crystal orientation of the wafer material. To plate a wafer having a notch, the seal of the contact ring must have an inward protrusion at the notch. During electroplating, electric current is concentrated at the notch due to the irregular geometry. This causes the plated film to be thicker around the notch than on the rest of the wafer. The yield of the wafer may therefore be reduced since the thicker plated film around the notch may negatively affect subsequent processing steps.
Accordingly, engineering challenges remain in electroplating wafers and similar work pieces having a notch or other edge irregularities.